Separating sheet material



Patented Oct. 15, 1935 2,017,449 snranarmo SHEET MATERIAL- Herbert L. Thompson, East Pepperell Mass assignor to Nashua River Paper Company, East Pepperell, Masa, a corporation of Massachusetts No Drawing. Application May 3, 1933,

Serial No. 669,207 2 Claims. (01. 91-68) This invention relates to the manufacture of sheet material adapted to be used for separating sheets having a tacky or adhesive surface to prevent such sheets from sticking together when 5 they are being handled or while they are being stored or transported.

Material of this type is sometimes referred to as separating sheets or as slip sheets or as liner material and in the manufacture of sheet rubber or rubber-coated sheet material or other sheet material which has a tacky or adhesive surface, it is the common practice to use such so-called separating sheets or "slip sheets between the sheets with the tacky or adhesive surface to prevent them from adhering together. If the sheet material is to be rolled up into a roll for storage or transportation purposes it is also customary to roll a web of so-called liner material with the web having the tacky surface to prevent the layers of the roll from adhering.

A desideratum of a sheet material to be used as a slip sheet or as liner material is that it must be easily separated from the sheet having the adhesive surface without leaving any fibre or coating attached to the adhesive surface, and another desideratum is that such a sheet of liner material should be sufiiciently heat resistant so that it can be used for separating superposed sheets that are to be passed through calender rolls.

It is one of the objects of the present invention to produce a separating sheet or slip sheet which has these desirable characteristics.

My improved slip sheet or separating sheet may 35 be made from a felted fibrous material, such as paper, or from a woven fabric and in carrying out my invention I treat the sheet material, whether in the form of a felted sheet, such as paper or in the form of a woven fabric, with a 40 coating solution containing silicate of soda which results in providing the surface of such sheet with a film having a hard smooth surface somewhat in the nature of a glazed surface. I also propose to use in the coating solution an ingredient which gives flexibility to the coating film so that it will not crack when the sheet is folded or flexed. Glycerine or some glycerine substitute, such as hydrolized sugar, is suitable for this purpose. I also find that good results are obtained by adding to the coating solution a wax dispersion or wax emulsion. Such wax dispersion or wax emulsion tends to give the film a slippery surface and prevents the glycerine or its equivalent from drying out. The presence of the wax dis persion or wax emulsion further improves the 5 flexibility of the coating film.

While the proportions of these ingredients may be varied I find good results are obtained from a coating solution made according to the following formula:

' Parts by weight Silicate of soda, 42 Baum 140 Glycerine or hydrolized sugar or its equivvalent Sufiicient water to make the solution of a 1 proper working consistency.

I find that about 35 parts by weight of water makes a satisfactory solution.

These ingredients are mixed together under ordinary temperature conditions.

As stated above the separating sheet embodying the invention is made by coating a fibrous sheet with this coating solution. The fibrous sheet, whether in the form of paper or in the form offabric, may be coated on one or both sides, depending upon the use to which it is to ,be put and the coating may be accomplished by any of the coating methods now commonly employed for coating paper or fabric, such for instance as passing the sheet through a coating machine or by spraying the coating material on the sheet or even by passing the sheet through a bath of the coating material.

After the coating material has been applied to the sheet then the coated sheet is dried in any usual way and is rolled up into rolls ready for use as a separating material.

A separating sheet embodying this invention will not stick to rubber-coated goods or rubber goods and will not be injured by the application of heat. The separating sheets can, therefore, be usedin calendaring operations for maintaining sheets of rubber separate while passing through'the calender rolls.

A sheet of paper or cloth having this improved coating material applied thereto presents a smooth continuous film surface free from pro-' jecting fibres. In the application of the coating material to the paper or cloth the surfae fibres of the sheet material will be laid and buried by the coating film so that the surface of the coated fabric presents a smooth unbroken surface which is highly desirable in a separating sheet.

While I have referred above to the use of both glycerine or its equivalent and a wax emulsion or a wax dispersion yet both the glycerine or its equivalent and the wax emulsion or wax dispersion are not necessary as for some purposes a satisfactory separating sheet can be made by using either the glycerine ingredient or the wax emulsion ingredient. Both these ingredients reduce the brittleness which the silicate of soda. ingredient tends to give to the film and renders the coating film sufliciently flexible so that it will not crack when the sheet is flexed or folded.

Glycerine and hydrolized sugar are both hygroscopic in character and by virtue of this characteristic the presence of the glycerine or other hygroscopic ingredient prevents the coating solution from drying out to such an extent as to become sufi'iciently brittle to break or crack when flexed or folded. In the case of the inclusion of the wax emulsion or wax dispersion it is the waxy characteristic of this ingredient which imports the desired flexibility into the coatin solution.

Hence while for many purposes it is desirable to have both the glycerine ingredient and the wax emulsion ingredient in the coating solution yet the invention would not be departed from if one or the other were omitted. If either the glycerine or the wax emulsion ingredient were omitted then the proportions of the other ingredient would have to be sumciently increased to give the sheet the necessary flexibility.

In the description aboveand in the claims the term coating" is intended to include not only a 5 surface covering but also partial or complete impregnation.

A separating sheet made in accordance with this invention has the advantage that it is relatively inexpensive to manufacture so that by means of the invention slip sheets or separating sheets can be inexpensively made which are in the nature of single service sheets.

As stated above a separating sheet embodying my invention may be coated on one or both sides depending on the use to which it is to be put and by the terms coating or surface coated or coated as used in the claims I intend to cover a sheet which is coated on one side only or on both sides.

I claim.

1. Material for use as a separating sheet comprising a flexible fibrous sheet coated with a coating solution containing approximately 140 parts by weight of silicate of soda, 15 parts by weight of glycerine, and a relatively small amount of wax emulsion.

2. Material for use as a separating sheet comprising a flexible fibrous sheet having a film-like surface coating containing silicate of soda and glycerine in the proportions of approximately ten to one and also containing a small amount of wax emulsion.

HERBERT L. THONEPSON. 

